The present invention relates to an electric machine                wherein the electric machine has a stator and a rotor shaft,        wherein the rotor shaft is mounted in such a way that it can rotate relative to the stator about a shaft axis, with the result that the shaft axis defines an axial direction, a radial direction and a tangential direction,        wherein a rotor, which interacts electrically with the stator, is arranged on the rotor shaft,        wherein the rotor has at least one axially continuous rotor axial channel,        wherein the stator has a stator laminate stack, which extends over the rotor, when viewed in the axial direction,        wherein the stator laminate stack completely surrounds the rotor, when viewed in a sectional plane orthogonal to the axial direction, with the result that a closed rotor interior is formed, when viewed in the sectional plane,        wherein in each case one cover is positioned axially on both sides on the stator laminate stack,        wherein at least one of the covers has a central cutout through which the rotor shaft passes,        wherein the stator laminate stack has at least one stator axial channel, which is continuous when viewed in the axial direction and is completely closed when viewed in the sectional plane.        
Such electric machines are provided with protection class IP 55, inter alia. In this configuration, the electric machines generally do not have a housing.
In the prior art, a coolant, usually air, flows through the stator axial channels. The stator is cooled by means of the coolant.
However, excess heat is produced not only in the stator, but also in the rotor. In the prior art, it is not possible to cool the rotor directly. The excess heat produced in the rotor therefore needs to be dissipated via the air gap between the stator and the rotor and the stator geometry. As a result, the excess heat produced in the rotor can therefore only be dissipated to a limited extent. Owing to this circumstance, the electric machine can only be operated at a considerably reduced machine performance in comparison with a comparable electric machine in which the rotor is cooled directly. The reduction in the machine performance is up to 60%.
In the prior art, the poor cooling is often accepted since no solution is known for providing improved cooling of the rotor in a simple manner without needing to give up the high IP55 protection class.